Stoker



Nov. 14, 1944.

. c. WRIGHT 2,362,604

STOKER Filed NOV. 10. 1943 Patented Nev. 14, 1944 UNITED STATE-s PATENTOFFICE Calvert (J. Wright, vState College, Pa., lainlignol' to P Aiernsylvania Bituminons Goal con. Pa.. a corporation ollcnnsylvaniaBiosearch, Inc.,

Application November 10, 1948, Serial No. $09,651

f zillalms.

This invention relates to stokers, moreparticularly to underteed stokerswhich operate on the principle of partial oxidation of coaly prior toits undergoing active combustion. t

Underi'eed stokers as ordinarily constructed do not operatesatisfactorily'with strongly coldng ooa1s.-such as the Pennsylvaniacoking coals.

'.l'hat is, when itis attempted to burn a strongly coking coal in anunderfeed stoker o f customary construction there is4 a strong tendencyior'unburned coke to beformed and to accumulate and build up above theretort in' a generally columnar form known as a coke tree. Coketreosburn primarily at the bese, -and the presence of a coke tree results inunsatisfactory combustion, espe cially when the demand on the heatingunit is not'great. it slows down the response of the furnace to demandfor heat and causes over-shoot ing of thermostatic control. and it makesit diiilcult to maintain low hoid-ilre rates without dangel-.of the nregoing out, In fact, coke tree formation may become so extensive asactually to extinguish the iire or to push operi the furnace door.

A method of and apparatus for avoiding the formation of coke trees from,coidng coals .by

mildly oxidizing the coal before .active combustion begins are describedand claimed in an application'illed by Theodore S. Spicer and Calvert C.Wright on April 15, i941, Serial No. 388,626, and Aowned by the presentassignee.' More in detail, as the coal moves upwardly into and throughthe lower end of the retort of the stoker it is heated Aby conduction orheat downwardly from the actively burning coal, and in that portion of'the. column of coal in which the coal is heated but is not yet plastic,i. e., where coking has not beg'unt he coal is oxidized toon cxtentsuchas to-reduce but not destroy its coking power.

oxidation is chieily a surface phenomenonbut does not involve'activecombustion; This is aocomplished by introducing an oxidizing agent, moetsuitably air or an air-stream mixture into the coal at a point or in aregion euehthat'it comes into intimatel contact with the heated butnon-plastic coal. For brevity this procedure is referred toas apre-oxidationmethod of operating astoker. or as the preoxidationprinciple.

Extended experience has demonstrated amply that the precxidation methodeasily and imtis'fac--H` torily represses 'coke tree formation providedcertain critical details are observed. In the iirst place, the coalmustbemixed intimately with the oxidizing agent ,Is it moves upwardlythrough the preoxidationsone. Seoondasthecoal is mixed 66 ber is 4 thepreoxidation zone,

tial uniformity of coal size distribution across the section whilemixing it intimately with the oxidizwith the air or if the airdistribution is not.- uni.

form due to channeling oriscgregation of the coal into regionscontaininglargely iines and regions containing largely coarse particles. And asindicated abete. the coal must be heated but not suicientlv to render itplastic, and enough oxidizing agent must be supplied to produce thedesired oxidation before coking of the coal begins.

Although the necessary elevation and mixing of the coal withoutsegregation in the preoxidation zone maybe a/ccompliehedsatisfactorilyin various ways, the 'simplest and most eil'ective means for doing so isavertical screw. Likewise, although the oxidizing agent might beintroduced into the coal at any point prior tothe preoxidation none, itis preferred to supply the oxidizing agent throughs supplementary, orpreoxidizing, tuyl'eY situated below the regular or active combastiontoyres at a distance such that the agent enters the coal substantiallyat the lower end oi" It has been found in vactual practice that in theoperation of such a stoker there is a tendency for coal to 'enter thesupplementary tuyl'e. even to the extent of closing the tuyre opening.This w w. the amoimt of air is serious because it supplied by thesupplementary tn yre to the coal and coke trees result bccausethe coalis not oxidined sumciently.4 Moreover, continued operation and by' maycompletely lill -the tuyrel o forcing coal through the tuyre use thewind box to be'fnlled with liddlings, which. is objectionable` Aoopending application iiled by Speer W. Guthrie on November 64.1948.8ierla1 No. 509.011, also owned by the present assignee. disclosesand claims means for alleviating` the foregoing dimcuity. According tothat invention the supple'- v:military tuytre is constructed to have acontinuously unobstructed opening 4for rotation therein ons`scrapermember which acts to clear coal from The embodiment-shown intheape plication includes a vertical screw. for elevating i v the coal, anda hooked.4 or claw-like, scraper memconneoted`to the edge' of the 'lcxewblade so as to move in the tuyere opening when the screw is inoperation. As far as I am aware the construction described was the iirstmeans to be provided which atiorded any degree oi relief imm theaforementioned diiiicuity oi coal riddlings in the supplementary tuyre,Experience with it has shown that it acts to sweep riddiings from thetuyre, thus permitting the tuyre to serve its intended functioneiiicientiy, but that equally it has a tendency to push a portion oithe-riddlings into the wind box. While not an insuperable obstacle, thattendency is undesirable because it necessitates periodic cleaning of thewind box and. particularly with domestic stokers, stoker builders seekto eliminate such upkeep requirements as i'ar as possible.

The maior object of this invention is to provide a stoker constructedand operated in accordance with the preoxidation principle with simpleand inexpensive scraper means for automatically keeping thesupplementary, or preoxidation, hiyre free trom coal. and which does somore efi'ectively than is accomplished by the means propocedheretofore.

Otherl objects will appear from the foliowin! description. v

The invention will be described with reference to the accompanyingdrawing in which Fis. i is a vertical sectional view through thesignificant part o! a preoxidation'type stoker constructed in accordancewith one embodiment of the. Present invention: and Fier? a horizontalsection taken on line lI-II, Fig. i. r,I have discovered, and it is uponthis that the present invention is predicated, that the tendency ot ascraper carried by the screw night, or blade,

to push coal from the supplementary tuyre into' the wind box can berepressed. and .the obiect o! the invention attained, by mounting thescraper so that it lags the horirlontall component or the upwardthrusting action or the elevating screw. In accordance with theinvention this is accomplished by connecting the scraper to the shaft ofthe vertical screw at a position such that the eievatln action of thescrew leads the action o! the scraper. 4

Having reference now to the drawing, there is shown a preoxidation typeo! stoker comprising a other oxidizing agent from a main air duct i inany suitable way, as by a motor driven blower.

Coal is introduced to the retort by a horizontal,

screw I operating in a conduit 1. The blower which supplies air to mainduct t and the screw conveyor i are operated in any suitable manner;such drive means iorm no part of this invention and because they arewell understood in the art they do not require illustration or furtherdescription.

Coal is delivered by lscrew conveyor t to the bottom o! the retort whereit is pickedv up and moved upwardly by a screw iiight t mounted on avertical shaftl la operated. by a gear l and a pinion i. which maysuitably be driven by the motor which operates screw I. "During vthe onperiods of the stolzer screw conveyor ii moves the coal progressivelyand continuouslyl upwardly through the retort into the .activecombustion acne-and in so doing the eoaiis mixed without mation o1'particles or pieces of varying sizes.

- which air is supplied tothe main combustion tuyres l and I. and alower air chamber Il through which air is supplied to the preoxidation ptuvre Il. Chambers I2 and Il act as conduits tor supplying air to themain and supplementary tuyres, respectively. Mounted at the juncture ofwind box I and the main air duct for pivotal movement about the end ofpartition Il is a butterily valve IB. By moving it appropriately,l asindicated by the broken line positions, Fig. 1, the air supplied throughduct 5 may be apportioned in. any desired `manner between the upper andlower air ,chambers i2 and I3. Thus, all of the air may be passed to theupper tuyres 2 and 3, or all of it may be passed to the preoxidationtuyre I4. In ordinary practice, however, valve I! will be adjusted tosupply an amount of air to the preoxidation tuyre i4 which eii'ectspreoxidation sumcient to prevent coke tree formation, and oir necessaryfor combustion is passed directly to the active combustion zone throughupper air chamber I I and tuyres 2 and 3. A smokeback opening I0 may beprovided as shown in FigVl for the usual purpose of preventing backpressure at, this point.

' The upper, or active combustion, tuyres 2 and I are. as will beobserved from Fig. i. of the usual sectional construction which forms aseries of spaced openings between webs la and 8a. `The preoiddationtuyreil has. however, a continuously unobstructed opening,4 as shown in thedrawing,'to permit a scraper member to enter-'and to pass completelyaround the tuyre opening to sweep from it any piecesot coal that mayndtheir way into it.

In the embodiment shown the scraper comprises 'a scraper blade Ilcarried by an arm It which is seated in a bore in the vertical screwconveyor shaft l and is held rigidly in place in any suitable way, as bya set screw iii.

The present invention is predicated, as indicated above, upon aparticular mounting of the scraper I1. To this end the arm which carriesthe scraper is connected to the vertical shaft Ba at a level such that4the scraper blade will move through the opening oftuyre I4, and it is soretort 'I oi conventional form provided with one or more main combustiontuyres which iorm the positioned with respect to screw ilight 8 as to beoiiset with respect thereto, i. e., to lag the horinontal component ofits upward thrusting action in the plane oi the tuyre opening. suitablyby about one-fourth turn. Most suitably arm is is connected to shaft laat a point not iarfbeiow the iiight-and the iiight is operated so thatthe g area just above` and below the arm is open. The

, the active combustion -zone.

scraper then acts immediately after the screw has exerted its maximumtendency to push coal `into the openingoi' the preoxidation tuyre.

The operation of e.l stoker constructed in accordance with the drawingwill -beunderstood from what has been said above. Briefly, during the onperiods of the stoker coal from a hopper or bin, not shown, passesthrough conduit 1 to the bottom of the retort and is there picked up byscrew conveyor I and moved Vupwardly toward Air for preoxidation enterstuyre i4, which is situated at a level such that the temperature of thecoal is sumcient for initiation' of the desired preoxidation butinsuriicient to make it plastic. Under the combined action of mixing byconveyor l, with avoidance of segregation of iines, and of the airintroduced through tuyrev Il, the coal is suiiiciently oxidized. by thetime it reaches the plastic zone, which lies aseaeoe at or immediatelyabove the upper end o! conveyor il, that coke trees do not form when thecoal burns in the active combustion zone. i. e., in the region o! tuyresI and I.

Meanwhile, rotation oi' screw ilight B continuously moves scraper I1through the opening of tuyre I4. In consequence oi' the positioning cithis' scraper and the action of its leading edge. it acts continuouslyto sweep rlddlings from tuyre I4.

Various modifications are, oi course, permissible. For example, theleading edge of the scraper member may be shaped inother ways than shownin the drawing, or a plurality of scrapers o! the type and mounted asdescribed might be provided at spaced intervals.

According to the provisions of the patent statutes, I have explained theconstruction and mode or operation of my invention and have illustratedand described what I now consider to represent its best embodiment.yHowever, I desire to have it understood that, within the scope of theappended claims, the inventionvmaybe practiced otherwise than asspecifically illustrated andl described.

I claim:

1. An underfeed stoker comprising the combination of a substantiallyvertical retort provided with a main combustion tuyre at the upperportion where active combustion occurs, means for supplying coal to thelower end of said retort, a vertical shait screw conveyor disposedin'said retort i'or moving coal upwardly in the retort while mixing itthoroughly and maintaining substantial uniformity oi size distribution,theupper Patent No. 2,562,6olr.

t shaft'` of said screw` conveyor to lag the horizontal CERTIFICATE orCORRECTION.-

end oi said screw being disposed below the plane of said tuyre, asupplementary tuyre having a continuously unobstructed opening disposedin the retort wall below said main combustion tuyre for supplying anoxidizing agent to the coal engaged by said screw in a region where thecoal is heated but not plastic, conduits Ior supplying said oxidizingagent to the said tuyres. and a scraper member extending into saidsupplementary tuyre opening and connected to the component oi the upwardthrust oi the screw in the plane oi' the supplementary tuyre opening.

2. An underieed stoker comprising the combination of a substantiallyvertical retort provided with a main combustion tuyre at the upperportion where active combustion occurs, means for supplying coal to thelower end of said retort, a vertical shaft screw conveyor disposed insaid retort for moving coal upwardly in the retort while mixing itthoroughly and maintaining substantial uniformity of size distribution,the upper end of said screw being disposed below the plane oi' saidtuyre, a supplementary tuyre having a continuously unobstructed openingdisposed in the retort wall below said `main combustion tuyre forsupplying air to the coal engaged by said screw conveyor means inaregion where the coal is heated but not plastic, conduits i'orsupplying air to the said tuyres, and a scraper member extending into'said supplementary tuyre opening and connected to the shaft of saidconveyor between adjacent turns or the flight;

CALVERT C. WRIGHT.

i November 11|., 19111;.

oALvEar c. WRIGHT.

It is hereby certifiedy that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 1,'first column, line )45, for the word "stream" read steam;' and that thesaid Letters Patent should be read with this correction thereinthat thesame may' e'onrom to the record or the esse 1n maratone office.Signed'and sealed this 20th day of liarch, A. D. 19,45.

(Seal) Leslie Frazer Acting Commissioner of Patents.

aseaeoe at or immediately above the upper end o! conveyor il, that coketrees do not form when the coal burns in the active combustion zone. i.e., in the region o! tuyres I and I.

Meanwhile, rotation oi' screw ilight B continuously moves scraper I1through the opening of tuyre I4. In consequence oi' the positioning cithis' scraper and the action of its leading edge. it acts continuouslyto sweep rlddlings from tuyre I4.

Various modifications are, oi course, permissible. For example, theleading edge of the scraper member may be shaped inother ways than shownin the drawing, or a plurality of scrapers o! the type and mounted asdescribed might be provided at spaced intervals.

According to the provisions of the patent statutes, I have explained theconstruction and mode or operation of my invention and have illustratedand described what I now consider to represent its best embodiment.yHowever, I desire to have it understood that, within the scope of theappended claims, the inventionvmaybe practiced otherwise than asspecifically illustrated andl described.

I claim:

1. An underfeed stoker comprising the combination of a substantiallyvertical retort provided with a main combustion tuyre at the upperportion where active combustion occurs, means for supplying coal to thelower end of said retort, a vertical shait screw conveyor disposedin'said retort i'or moving coal upwardly in the retort while mixing itthoroughly and maintaining substantial uniformity oi size distribution,theupper Patent No. 2,562,6olr.

t shaft'` of said screw` conveyor to lag the horizontal CERTIFICATE orCORRECTION.-

end oi said screw being disposed below the plane of said tuyre, asupplementary tuyre having a continuously unobstructed opening disposedin the retort wall below said main combustion tuyre for supplying anoxidizing agent to the coal engaged by said screw in a region where thecoal is heated but not plastic, conduits Ior supplying said oxidizingagent to the said tuyres. and a scraper member extending into saidsupplementary tuyre opening and connected to the component oi the upwardthrust oi the screw in the plane oi' the supplementary tuyre opening.

2. An underieed stoker comprising the combination of a substantiallyvertical retort provided with a main combustion tuyre at the upperportion where active combustion occurs, means for supplying coal to thelower end of said retort, a vertical shaft screw conveyor disposed insaid retort for moving coal upwardly in the retort while mixing itthoroughly and maintaining substantial uniformity of size distribution,the upper end of said screw being disposed below the plane oi' saidtuyre, a supplementary tuyre having a continuously unobstructed openingdisposed in the retort wall below said `main combustion tuyre forsupplying air to the coal engaged by said screw conveyor means inaregion where the coal is heated but not plastic, conduits i'orsupplying air to the said tuyres, and a scraper member extending into'said supplementary tuyre opening and connected to the shaft of saidconveyor between adjacent turns or the flight;

CALVERT C. WRIGHT.

i November 11|., 19111;.

oALvEar c. WRIGHT.

It is hereby certifiedy that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 1,'first column, line )45, for the word "stream" read steam;' and that thesaid Letters Patent should be read with this correction thereinthat thesame may' e'onrom to the record or the esse 1n maratone office.Signed'and sealed this 20th day of liarch, A. D. 19,45.

(Seal) Leslie Frazer Acting Commissioner of Patents.

